Wireless communication networks and the Internet network are expanding rapidly and their number of users is increasing. The GPRS (General Packet Radio Service) of the GSM (Global System for Mobile Communications) provides means for transferring information in packet switched mode in a cellular radio network. GPRS also provides an interface to other packet switched networks, such as the Internet network.
FIG. 1 shows the interconnections of a telecommunication network in a packet switched GPRS service. The main element of the network's infrastructure for providing GPRS services is a GPRS support node. GPRS support nodes are categorised into Serving GPRS Support Nodes SGSN which, in packet switched data transmission, correspond to the Mobile Switching Centers MSC of the GSM network, known in connection with circuit switched data transmission, and Gateway GPRS Support Nodes GGSN. An SGSN is a support node that transmits data packets to a wireless terminal MS (Mobile Station) and receives data packets transmitted by a wireless terminal through a Base Station System BSS, comprising base transceiver stations BTS and base station controllers BSC. In this description, the term wireless terminal MS is used to mean all terminals that communicate over a radio interface. Thus, a computer terminal that communicates through a mobile station or, for example, a radio card attached to the computer will also be referred to as a wireless terminal. The SGSN also maintains GPRS registers (not shown in FIG. 1) that contain information on the location of the wireless terminals that move within its service area. Typically, the SGSN is implemented as a separate network element. The GGSN that communicates with the SGSN provides a connection to and enables co-operation with other networks. Such networks are, for example, another operators GPRS (cellular) network or a private network such as, for example, a company's Intranet network, a public switched packet data network PSPDN such as the Internet or an X.25 network.
For a long time, the user of a computer terminal in communication with the Internet network has had the opportunity to retrieve multimedia components, such as pictures, text, short video clips and audio clips in electronic format, into his computer terminal from a server in the Internet. As data transfer rates increase and the properties of mobile stations improve, an interest in a multimedia messaging service and messaging services in general has now also been awakened in wireless networks. Networks that support packet switched data transmission, such as the GPRS network and 3rd generation mobile communication networks, such as CDMA2000 (Code Division Multiple Access) and WCDMA (Wideband CDMA) are, in particular very well suited for the implementation of multimedia messaging services.
A multimedia messaging service for 3rd generation mobile communication networks has been proposed which will be implemented in a manner similar to the Short Message Service SMS in a GSM network, i.e. substantially in a store-and-forward manner by transferring messages addressed to a wireless terminal, stored in a specific messaging server, to the wireless terminal when it can be contacted. Preferably, the messaging server is located outside the cellular network, for example, in the Internet.
In the following description, a GPRS network will be examined. A wireless terminal “attached” to the GPRS network can transmit and receive data if it has an active PDP-context (PDP=Packet Data Protocol). Activation of the PDP-context may be effected either at the request of the wireless terminal or the network. The PDP-context is activated between the wireless terminal and a GGSN.
The present GPRS specifications support a network-initiated PDP-context activation procedure which can be used to open a data connection before a message is sent to a wireless terminal from a messaging server in a packet data network, such as the Internet. But, according to the GPRS specifications, in order to support the network-intitiated PDP-context activation procedure, the wireless terminal must have a static (permanent) PDP address, for example, a static IP (Internet Protocol) address, which means that the use of dynamic IP addresses in connection with a store-and-forward messaging service would be prevented.
However, from the point of view of cellular network performance, the use of dynamic IP addresses is advisable because in this case a limited number of available IP addresses can be used more effectively than when using static IP addresses. However, dynamic IP addresses can only be used in connection with a messaging service for PDP-contexts where the initiating party was a wireless terminal (wireless terminal initiated PDP-context activation procedure).
The existence of an active PDP-context is only known to the wireless terminal in question, the SGSN serving it and the GGSN with which the PDP-context in question is active. If there is a desire that the messaging service should also operate using dynamic IP addresses, it is necessary to solve the problem of how a messaging server located outside a cellular network can determine whether the wireless terminal to which a message stored in the messaging server is addressed is ready to receive data, i.e. (in the case of a GPRS network) whether the wireless terminal has an active PDP-context with some GGSN.
International patent publication WO 98/19438 presents a solution for implementing a multimedia messaging service in a telecommunication network. The multimedia messaging system presented in WO 98/19438 comprises a multimedia message store, in which a multimedia message addressed to a specific user is stored. The user is provided with an opportunity to communicate the multimedia presentation properties of his terminal device to the multimedia messaging system, which translates said multimedia message either partly or fully, taking into consideration the multimedia presentation properties of the user's terminal stored in a database. After this, the multimedia messaging system sends the multimedia message to the use's terminal. One objective of the invention presented in WO 98/19438 is to provide one common message store, which can be accessed from more than one terminal and network type. WO 98/19438 concentrates almost entirely on the translation of a multimedia message, and it does not identify a problem relating to determining the readiness of a terminal to receive data.